Heretofore, cathodes suitable for operation in microwave devices have been made from mixtures of tungsten and iridium powders. The manufacture of such cathodes is described and claimed for example in U.S. Pat. No. 4,708,681 issued 11/24/87 and U.S. Pat. No. 4,735,591 issued 04/05/88.
A difficulty with such cathode manufacture is the relatively high cost of iridium.